An ethylene/tetrafluoroethylene copolymer (hereinafter referred to as ETFE copolymer) is a polymer having weather resistance and chemical resistance inherent to a fluoropolymer and flexibility inherent to a hydrocarbon polymer. Further, the ETFE copolymer is a material having a low refractive index, whereby reflection of light is little, and light transmittance is high.
Accordingly, the ETFE copolymer molded product is widely used as a material for e.g. an exterior film for system kitchens, a surface film of a white board for marker pens, a mold release film, an outdoor film, a member for displays or a protective film for solar batteries.
Since the ETFE copolymer is a fluoropolymer, the surface energy is low. Therefore, the contact angle to water (hereinafter referred to as water contact angle) is at least 100°. Accordingly, water droplets tend to be formed on the surface.
Therefore, in a case where an ETFE copolymer film is used as an agricultural film for e.g. a greenhouse, the film is likely to be fogged with water droplets condensed on the surface of the ETFE copolymer film, or water droplets may drop.
Further, in a case where the ETFE copolymer film is used for a member for displays or a protective film for solar batteries, and the film surface is fogged with water droplets, visibility becomes poor, or electric power generation efficiency becomes low.
As an agricultural film, which is made of a fluoropolymer having a low water contact angle and a high hydrophilic property (high antifogging property) surface, the following film has been proposed.
An agricultural film having a layer comprising a photocatalyst such as titanium oxide and silicon oxide, formed on the surface of a film made of a fluoropolymer (Patent Document 1).
However, light transmittance of such a film is low for the following reasons.
(i) The photocatalyst absorbs light.
(ii) The layer comprising titanium oxide and silicon oxide has a high refractive index, whereby the light reflection is large.